Conversion systems



March 25, 1958 Filed May 15, 1956 R. W. SCHUMANN CONVERSION SYSTEMS 2Sheets-Sheet 1 0 DIGITAL-T0- ANALOG (la CONVERTER F-0 lp-34 H48 C G O J20 28 NUMBER eeueauon OUTPUT 34 42 c G Z40 FIG-4 22 3,0 Y i NUMBERGENERATOR 38 c 6 0 0m ROL INVENTOR 24 7 ROBERT W.SCHUMANN ATTORNEYS 2SheetS -heet 2 m Oh m wZmQ mum 23 Z R. W. SCHUMANN CONVERSION SYSTEMSMarch 25, 1958 I Filed May 15. 1956 r I I I I I I I l I l l I I I I I lI I l INVENTOR wm w OQN 6528 w .23 2 @0853 mm a 52 5: mm I M ROBERTW.SCHUMANN III w 8 1 3N 2 c 5.

I -KW ATTORNEYS llnited. dtzates Patent aszassz couvnnsron SYSTEMSRobert W. Sic-humanist, Wheaten, lib, assignor to Sperry RandCorporation, New York, N. Y., a corporation of Delaware Application May15, 1956, Serial No. 585,6tl

7 Claims. (Cl. 349 347) This invention relates to analog-to-digital anddigital to-analog conversion systems and in particular to such systemsutilizing magnetic core arrangements sometimes referred to as magneticmodulators.

In many automatic control applications, it is desirable to convertanalog information from primary and secondary transducers into digitalform. The electrical information produced by several types oftransducers is of the small signal variety. Thus several types of analogto digital converters presently require intermediate D. C. signalamplification when operating with this class of transducers. This, or"course, introduces an additional source of data error into the system.Also the electrical output characteristics of different transducer typesvary considerably. Thus if one converter is to handle several sources ofdata on a time sharing basis, it is very desirable in certain situationsthat a particular converter be capable of encoding information fromsources having a wide range of output characteristics.

Many automatic control problems require equipments exhibiting a highdegree of accuracy coupled with a short response time and goodstability. Generally these requirements are diametrically opposed and acompromise solution is usually required in equipment design.

A primary object of this invention is to provide an analog-to-digitalconversion system using magnetic core devices.

A further object of this invention is to provide an analog-to-digitalconverter capable of operating in numerous data channels wherein theelectrical characteristics (which may vary considerably) of each channelis independent of all other channels and the analog data in any channelcan be weighted by the converter.

A further object of this invention is to provide a means to convert fromanalog to digital signals without requiring intermediate D. C.amplification of small transducer or analog signals.

Another object of this invention is to provide an analogto-digitalconverter with automatic zero and full-scale calibration.

A still further object is to provide a magnetic modulator type ofanalog-to-digital converter with exceptionally quick response.

Other objects and advantages of the invention will be apparent from thefollowing specification and accompanying drawings, wherein:

Figure l is a block diagram of a typical multichannel electronicanalog-to-digital converter.

Figure 2 illustrates the invention as applied to Figure 1.

Figure 3 shows an exemplary number generator control and numbergenerator circuit, and

Figure 4 is a chart pertinent to the circuit of Figure 3.

Figure 1 illustrates an analog-to-digital converter which may beconnected to any number of diiferent data channels even though theelectrical characteristics of the channels differ widely. For purposesof explaining this invention, only four data channels (not shown) arepresumed, and the outputs thereof are applied respectively to terminalslit), l2, l4 and 16. The data channel outputs are D. C. or analogsignals which are to be transformed into digital signals. This isaccomplished by insorting the signals from the different data channelsrespectively into comparators 18, 2t), 22 and 24. The output of eachcomparator is respectively applied to gating means such as gates 26, 28,30 and 32. In order for the ditlerent data channels to be time-shared,the gates are sequentially enabled at their respective enabling inputs34. from the corresponding comparator is applied over line as to numbergenerator control 38. As will later be explained, the output of thenumber generator control 38 determines whether the number beinggenerated in number generator it) is to be increased ordecreased inaccordance with the amplitude of the signal on line 36. The output ofnumber generator 4 on line 42 is a pulsating, digital signalcorresponding in amplitude to the amplitude of the D. C. signal appliedto the one of the comparators whose gate is enabled if the comparator isin balance. When the signal on line 44 is at such amplitude as to causebalance in the comparator, the digital manifestation on line 42 will becorrect. However, it the signal on line causes unbalance of a comparatorthe output of which is gated to line 36, number generator so compensatesfor such unbalance by increasing or decreasing its output acorresponding amount and applying the changed output to thedigital-to-analog converter 46 over line 5-8. The signals emerging fromnumber generator on line 28 are such that they may be summed by theconverter as to provide a D. C. or analog signal on line which isrepresentative of the digital signal on line 58 causing such analogsignal.

To illustrate a more specific embodiment of the invention, reference isnow made to Figure 2. The comparators l8, 2%, 22 and 24 may take theform of magnetic modulators having magnetic cores 18a, 20a, 22a and 24::respectively. The input terminals 10, 12, 14 and 26 each lead to arespective D. C. signal biasing winding so, the other end of which isgrounded. In addition each of the cores carries a comparative or secondinput winding 62 wound on each core in opposition to winding 6d andconnected in series with each other to ground. The cores are alternatelysaturated in opposite directions by application of alternating currentto winding 64 when the respective gates 66, 68, 76 and 72 are enabled bychannel selection signals on one of the enabling input lines 74. Thesource of alternating current which efiectively passes the gates is analternating current excitation generator 76 which may be of known type.The gates may be, for example, pentodes which are designed to operate onthe linear portion of their characteristic curve when enabled by asignal to a thin suppressor grid from line 74.

When a modulator is excited, an output signal is induced in therespective output winding 73 for the modulator. The output windings 78are connected in series to ground and at their other end via line $2 todetector 3% Output from any one of the modulators, as it appears on line32, will be an alternating output. If the current on line 44 is of suchmagnitude as to cause a magnetomctive force on any one of the modulatorcores equal but opposite to the magnetomotive force caused by the D. C.input to biasing Winding 60 on the same core, when said core is excited,the alternating output on line 82 will be symmetrical. That is, thepositive and negative amplitudes of the signal on line 82 will be equal.However, if the magnetomotive forces produced by windings 6d and 62 on acore are ditierent so that the core is effectively magnetically biased,the output When any one of the gates is enabled, the output aseasse all?signal on line 82 will be asymmetric. Detector 34} will detect anyasymmetry in the output from any one of the cores and will provide asignal on line as correspending in amplitude from a predetermined orthreshold level, to the direction and amount of the net magnetic bias onthe excited modulator. That is, the deviation from said predeterminedlevel in one direction or the other is relative to the polarity of thenet magnetic bias, while the amount of deviation corresponds to theamplitude of the net magnetic bias. A detector of this type isillustrated and described in my copending application filed May 15,1956, Serial No. 585,008.

Number generator oil has a plurality of outputs indicated respectively 22 2 2 and may be a so-called forward-backward counter. When themagnetomotive forces produced by the current through windings so and aredifferent, the output of number generator control 3;? will cause thenumber generator 4% to change its contents a direction so as to approachan equality of magnetomotive forces in windings and 52 on the modulatorbeing excited. If the net magnetic bias produced by the currents inwindings as and 52 of an excited modulator is positive, the numbergenerator may generate a more positive number, for example. Conversely,then, when the net magnetic bias is negative, it generates a morenegative number to cause the magnetic bias to return to zero. Thedifierent output lines the number generator carry either a continuoussignal or no signal, indicating a l or a O or"; a digital system,respectively.

A specific embodiment of the number generator con trcl 33 and numbergenerator will now be described to clarify the forthcoming explanationof the operation of the digital converter 46.

Referring to Figure 3, the apparatus illustrated with in dash line 33'is the number generator control while the apparatus above dash line itisthe number generator The output on line 86 of Figure 2 from the detectortil) is applied to the 1 input side of a flip-flop see. This flip-flopis preferably of t e bi-stable type operative only when a signal ofthreshold amplitude is applied to one of its inputs. Therefore, when theoutput from detector 81) exceeds in amplitude said threshold level,flip-flop tilt) is set to provide an enabling output on line 162 to gateIltld. flowevcr, if the output from detector till of Figure 2 does noterrced tle threshold level, flip-flop ill!) will be set to its positionby a resetting impulse applied to line lilo. A reset pulse reaches linetee from line via gate ltlfi when the is enabled by an output from the0" side of monostable multivibrator 111. A signal of threshold mplitudeor greater on line 86 temporarily triggers t multivibrator ill to its 1state in which it st ys just long enough to prevent the immediatelyfollowing reset pulse on line lib? from setting flip-flop bacc to 0.However, if the next pulse on line 36 is of less than thresholdamplitude, multivibrator lit will enable 3% and allow the followingreset pulse to set flip-flop 1% to 0. Therefore, it is apparent that thereset pulses on line M7 should occur with the same frequency as theoutput on line $6, but approximately 186 out of phase therewith.

An output resulting ironan impulse on line res provi an output on lineto enable gate Periodic timing impulses are applied to terminal 112 andellectiveiy pass gates 1% and ill) when the gates are enabled. Thesignificance of a timing impulse through gate 164 is such that thedigital binary number from generator at is caused to increase by 1,while a timing pulse thro gh gate accomplishes a subtraction of l l nthe digital number in the generator 4 2. The fre- 5 .hty the timingpulses as compared to the frequency the reset pulses or the output online 86 varies versely with the accuracy resulting, i. e., the moretiming pulses presented to terminal H2 while flipflop is in either ofits states, the greater will be the number change and vice versa. Withonly one timing pulse per cycle of reset pulses, the generated numberwill change only by 1. Under any frequency of timing pulses, thegenerated number will actually oscillate around the true digital value.

The number generator 4% is composed of a flip-flop lid for its 2 stage,flip-flop lid for the 2 sta e, flip-flop 11$ for the 2 stage, etc., forwhatever remaining stages are in the generator. Each of these flip-flopsis of the type which may be set to its 1 state by an input on lines 12-9or to its 0 state by input on clearing line lZZ, while an input on line124 will toggle the state of the flip-flop from 1 to O or vice versa.Connected to lines 124 respectively are or circuits 25, each of whichhave two input lines 126 and 128, a signal on either of which willprovide an output on line 1124 to toggle the respective flip-flops. Eachof the flip-flops 314-, 116 and 116 has a gate 136 connected to its 0output line and a gate 132 connected respectively by lines 134, 136, 138to the 1 output sides of the flipllops. The 0 output lines of flip-flopsH4, 116 and ill; are connected respectively to the 2, 2 2 output lineswhich are also illustrated in Figure 2. For providing a di ital output,lines 134, 136 and 138 connect respectively as enabling inputs to gates140, 142, and M4 which, when enabled, transmit a digital pulse from thecommon input line 146 to the output lines 42a, 42b and 420,respectively. These output lines together with like lines, it any (notshown) comprise output line 42 of Figures 1 and 2.

In operation, number generator 49 of Figure 3 proceeds to follow thebinary number table set out in Figure 4. For the three digital stagesillustrated in Figure 3, there are eight possibilities of digitalcombinations at their output lines. Of course, for more stages therewould be more output combinations, and in fact, there would be 2 cutputcombinations where n represents the number of stages. In the chart shownin Figure 4, each column represents a stage with the one on the rightbeing headed 2 while the columns successively to the left are headed 2and 2 respectively. The number generator may be initially set torepresent any desired number by proper signals on lines 129, but to showthe operation thereof it will be assumed that a pulse has been receivedon the clearing line 122 to set all the flip-flops to 0. From thencetiming signals through gate ill-t of the generator control 38 willsuccessively set the flip-tlops to the binary values indicated in eachli -e 1 through 9 in the chart of Figure Similarly, a timing impulseissuing from gate ill? of the generator control 33 will cause asubtraction and the number generator upon successive receipt of suchpulses follows the binary numbers as illustrated in Figure 4 from thebottom of the chart upwards line by line. Therefore, the generator 4Gwill increase or decrease its binary number in accordance with whether apulse is received on lines or 1% to the flip-flop ltll) in the generatorcontrol Another embodiment of a forward-backward counte' ich may beutilized with this invention is discussed beginning at page 42 of theProceeding of the ACM of May 2 and 3, 1952.

With the operation of the number generator control in mind, it will beapparent that the outputs on lines 2, 2 2 etc. in Figure 2 represent ls0r Os depending upon the presence or absence of a signal, respectively,on each line. The grids of the respective vacuum tubes 156, 162, res,and are connected respectively to the 2, 2 2 and 2" output lines and theO or level of voltage thereon will determine whether or not therespective vacuum tubes will conduct space discharge current. The vacuumtubes are connected in parallel to a source of voltage B at terminals163 and 173, the former being 33-}- and the latter B-. The current fromterminal 163 flows through a plate resistor 172 to the vacuum tube whichis made conductive. However, the amount of current for each vacuum tubeis diflerent and is regulated by the size of the plate resistors 172.For the resistor 172 connected to tube 166 whose grid is connected toline 2", the value of resistor 172 is regulated to be R ohms. The plateresistors for the tubes connected increasingly to the number generatoroutputs corresponds inversely in value to the power of two times R ohms.That is, resistor 172 for tube 160 has a value R times 2", the plateresistor for tube 162 has a value of R times 2"- the plate resistor fortube 164 has a value of R times 2 etc., to R for the plate resistor fortube 166 in the nth stage of the number generator output. Connectedbetween the plate resistor and the plate electrode of each vacuum tubeis the anode of a diode 174. The cathodes of these diodes are connectedin common to line 44.

The converter 46 as thus described is a current summation device. Sincethe plate load resistances vary as the power of two, the currents drawnthrough the resistors, respectively, vary also as a power of two whenthe vacuum tubes are non-conductive. When any vacuum tube is conducting,its associated diode 17 i is cut off so that no current is providedtherethrough from the associated precision resistor 172 to line 44. Thedigit positions in the number generator iii which contain a 1 cause theassociated vacuum tube to be non-conductive. Thus, diodes 174 form acurrent summing circuit which produces a direct current corresponding tothe digital number in the number generator 41 It is apparent, then, thatdigital converter 46 sums the 1s in the number generator since the 0outputs therefrom prevent current through the corresponding diode 174.

Because the physical quantities being compared are actually themagnetomotive forces produced by the currents in the input Winding andthe reference current winding, it is entirely practical to choose, forany single modulator, the value of signal input current which is torepresent full scale. If the reference current is equal to I amperes atfull scale, and if there are N turns at full scale, then it is possibleto choose any reasonable value of full scale signal current by makingthe number of turns on the input winding such that the product of fullscale signal current times the number of turns on the input winding areequal to IN. Thus, one modulator of the multi-channel data convertermight employ 100 turns on the input winding and turns on the referencecurrent winding, whereas the reverse might be true for anothermodulator. Then the value of signal current which represents full scalefor one channel might be, for example, 1 milliampere, but for the otherchannel it would be 100 milliamperes.

Since the input signals might be in the form of voltages, such as is thecase where the measuring transducer is a thermocouple, it might benecessary to insure exceedingly high stability of the resistance of theinput winding. In such a case, a winding might be made using a wire suchas manganin, or platinum, which have predictable and small variations ofresistance with temperature, or predictable contact potentials willexist at the input terminals.

Thus it is apparent that there is provided by this invention a system inwhich the various objects and advantages herein set forth, among others,are successfully achieved. Modifications of this invention not describedherein will become apparent to those skilled in the art. Therefore, itis intended that the matter contained in the foregoing description andthe accompanying drawings be interpreted as illustrative and notlimitative, the scope of the invention being defined in the appendedclaims.

What is claimed is:

1. An analog-to-digital data conversion system comprising, at least onemagnetic core, a first winding on the core for carrying an input analogcurrent to be measured, excitation means for alternately driving thecore to opposing states of flux density, detector means coupled to thecore to respond to excitation thereof for detecting asymmetry of outputfrom the core, means coupled to the detector means for generating adigital number, means coupled to the digital number generating means forgenerating a corresponding analog current, and second winding means onthe core for carrying said generated analog current, the magnetizingforces applied to the core due to said respective currents being inopposition, the arrangement being such that differences in themagnetizing forces applied by the currents will cause shift in thedigital number generating means toward re-establishment of balance inthe magnetizing forces.

2. A system as in claim 1 wherein the means for generating a digitalnumber is a backward-forward mounting means having a plurality ofdigital outputs representative of the digital number, said countingmeans being responsive to the output of the detector means to add to orsubtract from the generated digital number an amount corresponding tothe direction and amount of unbalance of the magnetizing forces presentin the core.

3. A system as in claim 1 wherein: said means coupled to the digitalnumber generating means for generating said corresponding analog currentincludes current summaticn means for summing said plurality of digitaloutputs making up said digital number on a like plurality of digitaloutput cores.

4. Apparatus as in claim 3 wherein the current summation means includesa plurality of grid controlled tubes each one connected at its grid to adifferent one of said digital output lines, a plate resistance for eachof said tubes, said tubes being connected in common through therespective plate resistances to a source of voltage, each of theresistances differing from another resistance in value by a power oftwo, a plurality of unidirectional current conducting devices connectedrespectively to the plates of said vacuum tubes and in common to form anoutput line of said converter, the arrangement being such that thecurrent on said output line corresponds to the digital number generatedin said digital number generating means.

5. A system as in claim 1 including one or more additional magneticcores each having a first winding there on for carrying an input analogcurrent to be measured which may be diiferent from the currentspresented to the other cores, means for operatively coupling thedetector means to all of the cores to cause response of the detectormeans to the respective cores in predetermined time-sharing sequence,each of the additional cores having a second winding thereon to carrythe analog cu rent output from said analog current generating means atleast during response of the detector means to a given core, thearrangement being such that a plurality of cores may be utilized withoutduplication of the remaining recited component.

6. A system as in claim 5 wherein: the magnetic coupling of therespective windings to the respective cores are selected so that inputanalog currents within diflerent expected ranges for each core willnevertheless apply corresponding magnetizing forces to the respectivecores to match the magnetizing forces applied by the system generatedanalog current.

7. A system as in claim 5 wherein the number of turns of the respectivewindings on the respective cores is selected so that input analogcurrents within diiferent expected ranges for each core willnevertheless apply corresponding magnetizing forces to the respectivecores to match the magnetizing forces applied by the system generatedanalog current.

No references cited.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.2,828,482 March 25, 1958 Robert W Schumann It is hereby certified. thaterror appears in the above numbered patent requiring correction and thatthe eeid Letters Patent should read as cor rected below.

In the drawings, Sheet l in Figure 3 the numeral "20" in the upperleft=hand corner should be 2 m and the line interconnecting the junctionbetween output line 138 and gate 132 to the like junction betweenflip-flop 118 and gate 130 should be deleted; column 6, line 16, for"mounting read em counting o Signed and sealed this 12th day of August1958 (SEAL) Attest:

KARL Ha AXLINE ROBERT C. WATS Attesting Officer Comissioner of PatentsUNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Robert W, SchumannIt is hereby certified that error appears in the above numbered patentrequiring correction and, that the said Letters Patent should read ascor rected below.

In the drawings, Sheet 1, in Figure 3, the numeral "20" in the upperleft-=hand corner should be 2 and the line interconnecting the junctionbetween output line 138 and gate 132 to the like junction between flipflop 118 and gate 130 should be deleted; column 6, line 16, for mountingread counting Signed and sealed this 12th day of August 19580 (senAttest:

KARL Ha AXLINE ROBERT C. WATSON Attesting Officer Comnissioner ofPatents

